What causes melasma? The cause of melasma is complex. The pigmentation is due to overproduction of melanin by the pigment cells, melanocytes, which is taken up by the keratinocytes (epidermal melanosis) and/or deposited in the dermis (dermal melanosis, melanophages).
There are five total papillary muscles in the heart; three in the right ventricle and two in the left. The anterior, posterior, and septal papillary muscles of the right ventricle each attach via chordae tendineae to the tricuspid valve. The anterior and posterior papillary muscles of the left ventricle attach via chordae tendineae to the mitral valve.
The serous membrane (covering membrane) which, in humans and other vertebrates, forms the wall of the pericardial cavity and holds the heart in place. The pericardium is made of two thin layers of tissue. Immediately surrounding the heart, and attached to it, is the visceral pericardium, or epicardium. The heart can slide easily on the visceral pericardium, thus allowing it to beat freely.